Hi DVDTracker,

I assume you are talking PERL regexps?  There is slightly different syntax for different languages (various UNIX shells, xemacs, C language, etc).

The problem is anything in brackets means you are only matching one letter by default.

So your expression matches:
a&a.com
because it is finding a match with the underlined portion:
a&[u]a.com[/u]

If you are trying to match any alphanumeric for any number of characters, followed by the .net, .com, or .org domains, your expression should look like this:
[b]^[a-zA-Z0-9]+\.com|net|org$[/b]

I'm assuming the rest of your syntax is right. Offhand I forget how the logical or operator works (the |).  

The changes are the ^ anchor.  This anchors your regexp to the beginning of the word.  That was why your previous regexp was not excluding the "a&" portion in your example -- you didn't tell it that it couldn't have anything in front of the string you were matching.

The other change is the "+" modifier.  As I said earlier, anything in brackets denotes just one character.  So the + modifier means that you are now matching for one or more characters that meet the criterion of [a-zA-Z0-9].  If it was okay to have zero or more characters, you could use the * modifier instead of the +, but I don't think that is what you want in your example.

Hope that helps and it wasn't too terribly confusing.  Let me know if you need any follow up clarification.

Dilbert

[Edited to fix UBBcode]
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If it ain't broke, fix it till it is!

What your regular expression says is to find within the string a pattern that has one letter/number followed by a .com, .net, or .org at the end of the string.  Your string "a&a.com" matches that criteria.  It has an "a", which is a valid letter/number, followed by a ".com".  If you want your string to have only letters/numbers preceding the .com, etc., from the very beginning of the string, you need to write it thusly:

^[a-zA-Z0-9]+\.[com|net|org]$

I think that's right, although I didn't actually check it out myself.  YMMV.

DVDTracker, your last rule allows for invalid domain names that start with a - to still pass.   Below is the rule I developed years ago to look for valid e-mail addresses:

^[0-9a-z]([-_.]?[0-9a-z]\.?)*@[0-9a-z]([-.]?[0-9a-z])*\\.[a-z]+$

Boy, good luck with that working 100%. Now all you have to do is include all the national domains like ".co.uk" for commercial UK sites, etc, ad nauseum. You might try Network Solutions for a list of all TLDs.